The invention relates to monitoring the operational performance of fluid storage systems.
Large quantities of liquids and similar materials are often stored in bulk storage containers or tanks, which may be located above-ground, partially above-ground, or completely below ground. Such containers or tanks are generally connected by piping to flow-meters or dispensers.
For example, underground storage tanks (UST""s) and, occasionally, above-ground storage tanks (AST""s) are used to store petroleum products and fuel to be dispensed at automobile service stations, trucking terminals, automobile rental outlets, and similar operations through gasoline, diesel, or kerosene dispensing pumps. Fuel product is generally delivered to such facilities by a gravity drop from a compartment in a wheeled transport means such as a fuel delivery truck or an introduction of product through an underground piping system. AST""s or UST""s are often located at central distribution locations so that product can be subsequently withdrawn from the tank system to be transported for delivery to a variety of such facilities. A distribution location with UST""s or AST""s may receive deliveries of product from, e.g., a pipeline spur, wheeled transport, a barge, or a rail car.
Direct observation of the operating condition of such tanks and storage containers is difficult or impossible. The various methods for identifying the amount of product in tank systems have varying levels of accuracy, repeatability, and performance. Moreover, the accuracy of devices which measure the amount of product dispensed from the storage containers and tanks differs greatly, and may or may not be temperature compensated. The amount of product actually delivered to the tank system is often measured inaccurately and, frequently, not at all. Rather, the owner or operator of the tank or vessel usually records the invoiced amount of product delivered as the actual amount introduced to the tank system, without having any means of confirming whether the invoiced amount of product delivered is correct.
Consequently, effective management of such facilities is complicated by the numerous errors in the various measuring devices and procedures used to establish a baseline for management, planning and decisionmaking. Effective management requires the following:
1. Accurate measurement of the volume stored in the system.
2. Accurate determination of the volume dispensed from the system.
3. Accurate determination of the amount of product introduced into the system.
4. Identification of volumes added to or removed from the tank system which are not otherwise recorded.
5. Rapid identification of leakage from the tank system.
6. Continuous monitoring and diagnosis of the operating performance of all of the component measuring devices of the system.
7. Continuous analysis of sales data to predict demands of product from the system.
8. Determination of optimal reorder times and quantities as a function of ordering, transportation, holding, and penalty costs in order to minimize total costs of operation and/or to maximize profits.
Traditionally, these functions were performed crudely or, in many cases, not at all. Volume measurements were, and in many instances still are, based on imperfect knowledge of the geometry, dimensions, and configuration of the storage vessel. Also, dispensing meters are frequently miscalibrated. This is true even when tank systems are regulated, due to the breadth of tolerance permitted for individual sales as related to total tank volume. For example, deliveries from the delivery vehicle are almost always unmetered, additions of product from defueling vehicles are typically undocumented, and theft of the product is not uncommon.
Leakage of product has, in recent years, assumed a dimension far in excess of the mere loss of the product. Environmental damage can, and frequently does, expose the operator to very large liabilities from third party litigation in addition to U.S. Environmental Protection Agency (EPA)-mandated remediation which can cost in the range of hundreds of thousands of dollars. The EPA""s requirements for leak detection are set forth in EPA Pub. No. 510-K-95-003, Straight Talk On Tanks: Leak Detection Methods For Petroleum Underground Storage Tanks and Piping (July 1991), which is incorporated herein by reference.
To address these concerns, Statistical Inventory Reconciliation (SIR) was developed. The SIR method consists of a computer-based procedure which identifies all of the sources of error noted above by statistical analysis of the various and unique patterns that are introduced into the inventory data and, in particular, into the cumulative variances in the data when viewed as functions of product height, sales volumes, and time.
The present invention relates to an automatic SIR system that may continuously and automatically collect data from completely above-ground, partially above-ground, and completely below ground containers for statistical analysis. The invention addresses a variety of physical, business, operational and environmental issues associated with the bulk storage of liquids or pourable solids.
The present invention is an application of SIR that greatly enhances the ability to manage a facility effectively. It provides the means to characterize exactly the geometry, dimensions, and configuration of the storage vessel, identify overages and shortages in deliveries and unexplained additions and removals of product, and provide an accurate assessment of overall dispensing meter calibration. In addition, by accounting for such discrepancies, the present invention permits identification of leakage at rates less than 0.1 gallon per hour in all of its estimates to any prescribed tolerance. By increasing the number of measurements taken, the estimates can be derived at any desired level of tolerance.
The method of the present invention makes no assumptions as to the precision of any of the measuring devices used in various system configurations. Precision and calibration accuracies are derived from the data alone. Also, it is not assumed that the tank system is leak free; the leak status of the system is determined from the data alone.
The method derives tank geometry, dimensions, and configuration, and their impact on the totality of cumulative inventory variances, as a function of product height in the tank. Correctness of dispensing meter calibration is verified in a similar manner by testing for randomness of cumulative variances as a function of varying sales volumes. Having confirmed that such remaining residual variances are random, reflecting only the inherent random noise of the measurement devices, the present method analyzes departures of the cumulative variance from the bounds determined by the calculated random noise level. All calculations as to the volumes added, removed, metered or leaking are based upon extended successive, simultaneous observations of meter and gauge readings. The number of observations incorporated in each such calculation is determined by computing confidence bands for the parameters of interest and extending data collection as necessary to achieve predetermined tolerances.
For example, the method of the present invention is capable of distinguishing between continuous losses consistent with leakage and one-time unexplained removals of the fluid product from the tank. The method may be used to ensure the accuracy of computed delivery volumes, which are determined and reported with confidence boundaries calculated for estimated delivered quantities.
The method can also be used to control and monitor the accuracy of purchase costs of fluids such as petroleum which are delivered to tanks. For example, motor fuel retailers may be charged by wholesalers for either net or gross volumes purported to have been delivered. A determination that purchase charges are appropriate thus requires frequent simultaneous readings of sales, tank volumes and temperatures, which can be accomplished using the method of the present invention.
To accomplish these goals, the present invention involves estimating changes in product volume in a tank based on multiple data points and their respective likely errors measured continuously over a period of time. A software program is used to implement an algorithm that employs concepts from matrix theory and mathematical statistics. The algorithm includes generating the product of a matrix and its transpose by successive additions of partial products of partitions of the matrix and their corresponding transposed matrix partitions to minimize the storage requirements of the data collected. The compressed matrix data constitutes a complete and sufficient statistic for the parameters of interest. The algorithm thus permits the accumulation and storage of a large amount of data in a condensed form without sacrificing statistically useful information, to obtain a statistically significant result with the required accuracy and reliability.
In general, in one aspect, the invention features a method of monitoring a fluid storage and dispensing system including a dispensing apparatus. A quantity of fluid is dispensed from the system using the dispensing apparatus based on an authorization. A plurality of measurement data is collected from the dispensing apparatus in a form readable by a computer. The plurality of measurement data is stored in a memory. The stored plurality of measurement data are statistically analyzed to calculate a volume of fluid based on the plurality of measurement data collected from the dispensing apparatus.
Implementations of the invention may also include One or more of the following features. The authorization May be based on information relating to a user requesting that the quantity of fluid be dispensed from the system. The authorization may be provided by a fuel access control system.
The method may further include transmitting the plurality of measurement data to a processor to perform the statistically analyzing step. The plurality of measurement data may be stored in a compressed matrix format, which may be a product of a data matrix and a transpose of the data matrix. The dispensing apparatus may include a totalizer and a meter.
In general, in another aspect, the invention features a method of monitoring a fluid storage and dispensing system including a plurality of dispensing apparatus. A quantity of fluid is dispensed from the system using the plurality of dispensing apparatus based on an authorization. Measurement data is simultaneously collected from the plurality of dispensing apparatus in a form readable by a computer. The collecting step is repeated to obtain a plurality of the measurement data, which are stored in a memory. The stored plurality of measurement data is statistically analyzed to calculate a volume of fluid based on the plurality of measurement data collected from the plurality of dispensing apparatus.
Implementations of the invention may also include one or more of the following features. The authorization may be based on information relating to a user requesting that the quantity of fluid be dispensed from the system. The authorization may be provided by a fuel access control system.
The method may further include transmitting the plurality of measurement data to a processor to perform the statistically analyzing step. The plurality of measurement data may be stored in a compressed matrix format, which may be a product of a data matrix and a transpose of the data matrix.
In general, in another aspect, the invention features a fluid storage and dispensing system including a tank for storing fluid and a dispenser for dispensing fluid from the tank. A fuel access control system enables the dispenser based on an authorization. Measurement apparatus collects measurement data corresponding to a quantity of fluid dispensed from the tank by the dispenser. A processor statistically analyzes the measurement data to calculate a volume of fluid in the system.
Implementations of the invention may also include one or more of the following features. The system may further include a memory for storing the collected measurement data. The measurement apparatus may include a totalizer and a meter.
The fuel access control system may be activated by a coded medium which contains identification information pertaining to the user and which constitutes a request to dispense fluid from the system. The authorization may be based on information about a user requesting to dispense fluid from the system.
The processor may store the measurement data in a compressed data matrix format, which may be a product of a data matrix and a transpose of the data matrix.
An advantage of the present invention that the accuracy and consistency of devices used to measure volume of product added to, removed from, and present in a fluid storage system may be determined.
Another advantage of the present invention is that additions of material to the system, but not recorded as such, and volumes of product removed from the system which are not registered by measuring devices or otherwise recorded, may be identified.
Another advantage of the present invention is that discrete one-time unrecorded removals of product from the system may be distinguished from continuous losses consistent with leakage.
Another advantage of the present invention is that product leakage from all parts of the system, extending from the fill point to the point of discharge, may be identified and confirmed.
Another advantage of the present invention is that secular, seasonal trends and repetitive special demands to provide short and long term estimates for demand of the product, and optimal reorder quantities and delivery schedules, may be identified and determined.
Another advantage of the present invention is that a better estimation of product volumes and volume changes may be obtained by calculating the differential of the volume function.
Another advantage of the present invention is that a fuel access control system may be used to monitor dispensing activity from and control access to the fluid storage system.
A further advantage of the present invention is that all of the foregoing may be accomplished in a fully automated system that requires no human intervention, other than as an option available to the operator to enter quantities of material reportedly delivered for comparison with those computed.
Other features and advantages of the invention will become apparent from the following detailed description, and from the claims.